This invention pertains to fabrication of electronic devices such as integrated circuits; more specifically, this invention relates to methods of electroless plating solution management and electroless plating solutions.
Process control is a critical aspect of fabricating complex devices such as electronic devices. For devices such as integrated circuits, the process specifications and the process results must meet strict specifications in order to assure the desired performance for the integrated circuits. Not only is there the challenge of achieving desired process specifications and process results, there is the added challenge of maintaining those specifications and results for processing numerous substrates under, preferably, economical conditions.
In order to meet the requirements for electronic devices, processes such as electroless deposition have been adopted for applications such as depositing cap layers for copper-dielectric metallization structures. Electroless deposition processes offer selective deposition of cap layers such as cobalt-based cap layers and such as nickel-based cap layers. Some more preferred cap layers are multi-element alloys such as cobalt alloy, cobalt-tungsten alloy, cobalt-tungsten-phosphorous-boron alloy, cobalt-nickel alloy, and nickel alloy. The complexity of some of the desired compositions for cap layers requires complex reaction chemistries to produce those layers and there is a correspondingly complex problem in process control for process equipment such as electroless deposition equipment and associated electroless deposition bath.
Successful process control for electroless deposition equipment involves maintaining the electroless deposition bath within required specifications so as to achieve the desired process results. Typically, there is an acceptable range of specifications for operating the electroless deposition bath. Important parameters to be maintained during electroless deposition practice are deposition rate, bath stability, film composition, film coverage, and film roughness. These parameters are usually maintained by controlling the composition of the electroless deposition bath, particularly the amounts of reactants such as metal ion sources, reducing agents, and pH adjustors. When the loading in the deposition solution is high compared to the concentration of consumed bath components, the concentration of byproducts can quickly build up in the plating bath when the plating solution is used in a recirculation mode or a batch mode. This change in the electroless bath composition can alter the deposition process and, consequently, the deposition rate and some of the characteristic properties of the film.
There are known approaches to monitoring and maintaining the operation of electroless deposition baths. In most cases, the reducing agent concentration, the metal ion concentration, and the pH of the plating bath are monitored in addition to the temperature of the bath. In order to maintain the bath in a predetermined process window, chemicals have to be added to the bath if the reducing agent concentration, the metal ion concentration, and/or the pH are out of specification. One can maintain the bath by adding as needed pH adjustor, reducing agent, and metal ions. In addition to the concentration adjustment, fresh solution may be added to the plating solution from time to time since a part of the solution may be lost due to drag-out when the plated substrate is removed from the plating chamber.
Although methods of electroless deposition solution management and electroless deposition solutions are known, the present inventor has recognized a need for new and/or improved methods of managing electroless deposition solutions and new and/or improved electroless deposition solutions for electroless deposition of cap layers used to fabricate electronic devices.